Electromechanically actuated vehicle brakes are fundamentally known. Aimed at providing an efficient wheel brake of compact and lightweight construction, an electromechanical actuator comprises an electric motor and a multistage transmission, which serves to gear down an electromotive rotational drive movement from an electric motor of relatively lightweight and compact design, and to convert this geared-down rotational drive movement into the required translational movement in order to generate braking forces. To this end, the transmission comprises a spindle-nut-arrangement, which translates the rotational movement into a translational movement. For this purpose, the electromechanical actuator is attached on a single side to a stub axle-shaped brake housing, which accommodates one or more translationally displaceable pistons on the actuator side. The brake housing is arranged so that it is displaceable in relation to a carrier fixed to the vehicle. Utilizing the reaction forces whilst performing a relative displacement of the brake housing means that a single electromechanical actuator of low weight is in principle sufficient to apply brake linings arranged on both sides of a brake disk to friction surfaces of the brake disk by means of opposing translational movements, and with the required application force of approximately 1800 Newton.
It is often not fully appreciated in this context that for various reasons (application forces, temperature, fouling, operating reliability, weight, wear, ventilation capacity and many other influencing variables of a usual load spectrum) the demands placed on an electrically and hydraulically actuated motor vehicle brake are exceptional in the extreme and also subject to constraints in terms of the acceptable costs. In this context it must also be remembered, in particular, that a wheel brake cannot be regarded as a completely inelastic, rigid construction, but that when subjected to high stress-loading an elastic material behavior is inevitable, that relative changes in the position of adjacent components in relation to one another have to be catered for, and that modified, possibly wider geometrical and positional tolerances may be necessary.
In the case of so-called combined hydraulically and electromechanically actuated vehicle brakes performing an electromechanical parking brake function there is the further special feature that energy for actuation of the brake may be generated both electromechanically, hydraulically, or by a combination of these methods. For this reason, in a force flux between the spindle-nut-arrangement and the piston a releasable coupling is provided, which allows a purely hydraulic actuation without damaging or having a negative reactive effect on the spindle-nut-arrangement.
Known electromechanical parking brakes may have the following problems. Under unfavorable conditions in which the actuator travel is extended (thermal expansion, worn friction pairings or the like), rattling noises can be generated when running over rough roads. It has been determined through analysis that some of the causes of such rattling noises are to be sought primarily in the area of the components of the electromechanical actuators. This is because the dimensioning of inevitable geometrical and positional tolerances, clearance fits, particularly of a movement in a radial direction between components of the electromechanical actuators on the one hand and the piston on the other, are a source of these noise problems. A further finding was that the effects prompting complaints result in particular from oscillation phenomena in the area of a coupling between the spindle-nut-arrangement and the piston.